Transmitter apparatus



Nov. 29, 1949 w. J. PocH TRANSMITTER APPARATUS Filed July 26, 1945 01/TPl/P REUJC/LLATGR mmvroa. VVa/demdr a P001} BY I ATTORNEY.

Patented Nov. 29, 1949 TRAN SItflTTER APPARATUS Waldemar J. Pooh,Moorestown, N. J assignor to Radio Corporation of America, a corporationof Delaware Application July 26, 1945, Serial No. 607,110

3 Claims. 1

This invention relates to television transmitter circuits, withparticular emphasis being placed upon a circuit and system for moreefficiently providing plate modulation of the output stage under thecontrol of output sync or synthesizing signals.

In the past, provisions have been made for utilizing a cathode followertype of circuit to drive the plate voltage or an output power stage in amore positive direction to obtain high power outputs. Under suchcircumstances, however, it has been found that the output which isobtainable is dependent upon the maximum current obtainable from thecathode follower. Yet, even this did not provide an adequate amount ofpower under most circumstances because the current which was obtainablefrom the cathode follower in the prior art was usually limited by theplate load resistance of the preceding tube.

According to the present invention, provisions have been made whereby itis possible further to increase the peak current from the plate followerthrough the use of an addition-a1 cathode follower tube to drive theusual cathode follower serving to control the output tube. Thisarrangement is possible because it is so set up that current flowsthrough these tubes at a maximum value for but a very short interval sothat the plate dissipation of the driver tube is not exceeded.

According to the present invention, the sync driver tube is connected toreceive controlling, synthesizing or sync pulses arriving thereupon in apositive sense. The sync driver then serves as a low impedance drivingsource for impressing the synchronizing signal upon the grid or input ofthe sync modulator tube in cathode follower fashion. The sync modulatortube, in turn, is connected to deliver its output in cathode followerfashion to the output tube. There is also associated with the outputtube a capacity which is arranged to be charged through -'a suitablerectiher during the time interval that the sync pulses are removed insuch a direction that the capacity charges practically to a value whichis equal to that of the plate supply at the output from the syncmodulated cathode follower connected tube and is such that when thecontrolling voltage is positive on the sync modulator, it forces itscathode practically to the plate voltage and tends to add thus to thevoltage acquired by the condenser and so increase the output from thesystem.

In the light of the foregoing, it will be appreciated that one of themain objects of this invention is to provide in a more efficient mannerfor modulating an output stage for television trans- 2 pulses and thento drive the output tube in such a way that exceedingly high peakcurrent outputs are derived therefrom.

A further object of the invention is to provide a simplified modulationsystem for a television transmitter wherein it is possible to obtainexceettilngly high short duration peak output curren s.

Further objects of the invention are those of providing a more eflicientand yet simplified modulation system for television transmitters and thelike which overcome one or more defects of the prior art and which, atthe same time, avoid the limitations heretofore placed upon such appaandwhich may have developed from any suitable form of sync generator aresupplied at an input terminal I I. Purely by way of illustration,

sync signals which exist as pulses extending in the positive directionare shown in diagrammatic form immediately above the input terminal II.

There pulses, which are of relatively large amplitude, as indicated, arefed by way of the condenser B to be applied to the grid or controlelectrode l5 of a sync driver tube I1. This tube has provided therewiththe usual grid resistor H! which connects at one end to the grid orcontrol electrode l5 and at the other end to ground 2 I. Likewise, thecathode 23 of this tube connects to ground through the cathode outputresistor 25.

Suitable plate voltage for operating the tube is provided from a source(not shown) having its positive terminal connected at the terminal point21 and its negative terminal preferably connected to ground.

Output signals from the sync driver tube II are supplied across thecathode output resistor by way of the conductor 29 to the grid orcontrol electrode 3| of the sync modulator tube 33. This tube also hasits cathode 35 connected to one terminal of the cathode load or outputresistor 31 of which the second terminal also connects to ground 2|.Plate voltage for this tube is supplied at a terminal 21 from a sourcesuch as that connected at the terminal point 21.

mitters in accordance with the controlling sync 56 The output signalsfrom the sync modulator tube 33 are supplied in cathode follower fashionby way of the conductor 39 to the plates 4| and 42 of the output tube 43(only partially shown herein) by way of the condenser 45. This samevoltage is also applied to the screen grid electrodes 41 and 41' of theoutput tube 43 through the condenser 49. v

The control voltages which are applied to the plates 4| and 42 as wellas the screen electrodes 41 and 41 of the output tube 43 are supplied inpush-push fashion through the connection to the midpoint of the primarywinding 5| of a transformer 53 of which the secondary 55 connects to asuitable output or load circuit or further amplifiers (not shown).

The condensers 45 and 49 are adapted to charge through a diode 57 ofwhich the cathode 59 is connected to one terminal of condenser 45 and ofwhich the anode 6| connects to a terminal point 63 whereat positivevoltage is applied. The resistor 61 connected between the anodeconnection 5| and the screen electrode 41 and 41' serves as a screenvoltage (ropping resistor.

Not only may the sync signals be applied to the output tube 43 inpush-push fashion, as indicated, but the video signals developed in thesystem, as indicated at 69, may likewise be applied in push-push fashionto suitable inner grids H and II by way of the connection throughtransformer secondary 13 in purely conventional manner. A suitable radiofrequency oscillator of any desired character'and buffer arrangement,

conventionally represented at I5, may be used to supply output signalsby way of the transformer primary ll to feed the RF voltages upon theinner grids along with the video signals.

In accordance with the arrangement thus disclosed, it will be seen thatwith the positive sync pulse being applied at the input terminal H, thesync driver tube I! has itsgrid driven highly positive so as to draw aheavy plate current for the duration of the sync pulse. With the cathodefollower connection provided between the output of the sync driver tubel1 and the grid or control electrode 3| of the sync modulator tube 33,it will be appreciated that this latter tube also is driven far into thepositive region at times when a the sync pulse arrives at the inputterminal N. -This permits the sync modulator tube 33 to deliver a veryhigh peak current to the output tube 43. Even the duration of the peakpulse interval is short. Because of this short duration peak currentpulse, the average currents flowing in each of the tubes l1 and 33 arequite reasonable and it is possible to so arrange the system that thesync pulse controls the driver tube in such a way that a control is hadon the modulator tube while, at the same time, obtaining a high outputwhere the control comes from a tube which is driven to cut ofi most ofthe time and the control sync pulse is positive on the grid of themodulator tube.

With respect to the arrangement shown for charging the condensers 45 and49 through the diode 51, it will be appreciated that each of thesecondensers can charge during the time interval between successive syncpulses almost to a value which is equal to that of the supply connectedto the terminal 63, because for periods of conduction, the diode offersrelatively low resistance. Then, when the sync pulse is applied to themodulator tube grid 3| to cause a very high current to flowtherethrough, it forces the cathode of the modulator tube 33 topractically the voltage of the plate, and this voltage then obviouslytends to add to the voltage to which the condensers 45 and 43 have beencharged so as to become effective on the output tube 43.

The remaining connections of the output tube 43 have been omitted forreasons of simplicity of illustration, but purely by way of example andto show the general nature of the system hereinabove set forth, it maybe suggested that the sync driver tube may be of the type known as the6AC7. The sync modulator tube 33 may be of the type known as the 6V6.The output tube 43 may be of the double pentode variety, such as thepush-pull RF beam power amplifier, commonly known as the 8293. Lastly,the diode may be part at least of a tube of the general type known asthe 6X5. While the cathode resistors used to provide the cathodefollower connections are not critical in value, it has been foundconvenient in practice to provide the resistor 25 as one of about 1500ohms, while the resistor 31 is slightly larger and may be of thegeneralorder of 4000 ohms.

Having now described my invention, I claim:

1. A modulator circuit for modulating a television transmitter under thecontrol of applied synthesizing impulses which comprises, in succession,a driving tube, a modulator tube and an output tube, a cathode outputresistor for each of the driver andmodulator tubes, means for connectingthe modulator tube to the driver tube and the output tube to themodulator tube each in a cathode follower connection, means forsupplying control pulse energy to the input circuit of the driver tubeso that like polarity output controlling pulses are supplied upon themodulated electrode of the output tube, a condenser element includedserially in the connection between the modulator tube and the outputtube, a rectifier connected to charge the, said capacity element in thetime interval intervening between the application of successivesynthesizing impulses to the driver tube, and means xto render therectifier inoperative to charge the condenser during the period of theimpulse duration, whereby the voltage in the condenser effectively addsto the voltage applied to the output tube during periods of impulseduration and during periods of impulse interruption the charge in thecondenser applied through the rectifier approaches the voltage normallyapplied to the rectifier.

2. A modulator circuit for pulse output transmissions which comprises insuccession a driving tube, a modulator tube and an output tube, acathode output resistor for each of the driver and modulator tubes, acathode follower connection for connecting the modulator tube to thedriver tube and across the cathode resistor thereof, a cathode followerconnection for connecting the plate elements of the output tube to theoathode resistor of the modulator tube, means for supplying controlpulse energy of positive polarity to the input circuit of the drivertube whereby the polarity of the controlling pulse upon the modulatedplate of the output tube coincides with that applied to the input of thedriver tube, a capacity element connected between the modulator tubecathode output and the output tube, a rectifier connected to charge thesaid capacity element in the time interval intervening between theapplication of successive control pulses to the driver tube, and meansprovided by the pulse signal flowing in each of the driver tube, themodulator tube and the output tube to render the rectifler inoperativeto charge the capacity element during the period of the pulse duration,whereby the voltage in the capacity element efiectively adds to thevoltage applied to the output tube during periods of pulse duration andduring periods of pulse interruption the charge in the capacity elementapplied through the rectifier approaches the voltage normally applied tothe rectifier. r

3. A circuit for modulating a television transmitter output tube whichcomprises, in succession, a driving tube, a modulator tube and an outputtube each having at least a cathode, an anode and a control gridelectrode, a cathode output resistor connected to the cathode of each ofthe driver and modulator tubes, a cathode follower connection forconnecting the modulator tube control grid to the driver tube cathodeand across the cathode resistor thereof, a cathode follower connectionfor connecting an anode electrode of the output tube to the cathode andacross the cathode resistor of the modulator tube, means for supplyingcontrol pulse energy of selected polarity to the input circuit of thedriver tube whereby the polarity of the controlling pulse applied to theanode of the output tube coincides with that applied to the input of thedriver tube, a capacity element included serially in the connectionbetween the modulator tube cathode outconnected to charge the saidcapacity element in one selected direction in the time intervalintervening between the application of successive control pulses to thedriver tube, and means provided by the pulse signal flowing in each ofthe driver tubes, the modulator tube and the output tube to render therectifier inoperative to charge the condenser during the period of thepulse duration and during such period to cause the voltage in thecapacity element effectively to add to the voltage applied to the outputtube during periods of pulse duration and during'periods of pulseinterruption the charge in the capacity element applied through therectifier so that the charge approaches the voltage normally applied tothe rectifier.

WALDEMAR J. POCH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,103,362 Hansel! Dec. 28, 19372,289,243 Clough July 7, 1942

